Quote Originally Posted by blackraven
I totally agree. Spend your money on one really good amp and forget about bi-amping. Any benefit in sound from bi-amping may be marginal.
But a high quality amp would be better than 2 average amps.

For a 5.1 setup I would consider the parasound Halo A51 or A52. You can always add a 2 channel amp later for 7.1 sound.
http://www.parasound.com/halo/

Consider these monoblocks for rear channels, they are a steal at $270 a piece http://www.outlawaudio.com/products/2200.html

Hmm - quite interesting -- I could be guilty of irrational bi-amping exuberance.

Which spec numbers are the ones to look for in terms of head-room so I can compare?

I might have to go back and start over then, but I think I have kicked out the Marantz option and am down to the NAD and the Arcam -- unless I can find your Halo A51 used, it is probably out of my price range.